Insulating materials resistant to attack by molten metals, including aluminum alloys, are known to the prior art. For example, Moritz U.S. Pat. No. 3,212,142 discloses a process and apparatus for continuous aluminum casting. The apparatus includes a mold having an outer metal shell lined with an annular header or liner of insulating material. The insulating header is made from a composition wherein asbestos fibers are distributed in an inorganic binder.
Asbestos-containing insulating materials have performed satisfactorily in the aluminum industry for several years. However, it is now necessary to discontinue usage of asbestos-containing materials because of health concerns. Accordingly, there is presently a need for asbestos-free insulating materials suitable for use as headers in continuous aluminum alloy casting.
U.S. Pat. Nos. 4,773,470 and 4,897,294 to Libby, et al. disclose calcium silicate insulating materials containing delaminated vermiculite which are claimed to be suitable for use as headers in continuous aluminum alloy casting. Other insulating materials which are used for various purposes are as follows.
Barrable U.S. Pat. No. 4,101,335 claims a fire-resistant asbestos-free building board comprising mica or a mixture of mica and standard vermiculite distributed in a calcium silicate binder. Barrable U.S. Pat. No. 4,132,555 claims an asbestos-free building board comprising standard vermiculite distributed in a water-soluble binder containing organic reinforcing fibers.
U.S. Pat. No. 4,690,867 to Yamamoto, et al. discloses a xonotlite-type calcium silicate insulating material containing carbon fiber as a reinforcing fiber. Other asbestos-free calcium silicate insulating materials known to the present inventors are disclosed in U.S. Pat. Nos. 4,111,712 and 4,128,434 to Walter Pusch.
A principal objective of the present invention is to provide an insulating material suitable for use in continuous molten metal casting.
A related objective of the invention is to provide an asbestos-free insulating material.
Another objective of the invention is to provide an insulating material having good toughness and resistance to high temperature cracking.
Additional objectives and advantages of the invention will become readily apparent to persons skilled in the art from the following detailed description of our invention.